Fix Path bounding box, improve rendering logic

Fix for path bounding box and some changes in path rendering.

Paths calculated in this way goes well with the gradients. Now all gradients in this test svg looks correct
![image](https://cloud.githubusercontent.com/assets/1194048/4313215/7cdad3f4-3ec5-11e4-80ff-53ca31bcf109.png)

Perhaps better to describe parameters inline? Not in description on top?